As an example of a mobile communication system to which the present invention is applicable, a 3rd Generation Partnership Project Long Term Evolution (hereinafter, referred to as ‘LTE’) and LTE-Advanced (hereinafter, referred to as ‘LTE-A’) communication system is briefly described.
FIG. 1 is a diagram schematically showing the network architecture of an E-UMTS as an exemplary mobile communication system. An Evolved Universal Mobile Telecommunications System (E-UMTS) is an advanced version of a legacy Universal Mobile Telecommunications System (UMTS) and standardization thereof is currently underway in the 3GPP. E-UMTS may be generally referred to as a Long Term Evolution (LTE) system. For details of the technical specifications of UMTS and E-UMTS, reference can respectively be made to Release 8 and Release 9 of “3rd Generation Partnership Project; Technical Specification Group Radio Access Network”.
Referring to FIG. 1, E-UMTS includes a User Equipment (UE), eNode Bs (eNBs), and an Access Gateway (AG) which is located at an end of a network (Evolved-Universal Terrestrial Radio Access Network ((E-UTRAN)) and connected to an external network. The eNBs may simultaneously transmit multiple data streams for a broadcast service, a multicast service, and/or a unicast service.
One or more cells may exist in one eNB. A cell is configured to use one of bandwidths of 1.25, 2.5, 5, 10, 20 MHz to provide a downlink or uplink transport service to several UEs. Different cells may be configured to provide different bandwidths. The eNB controls data transmission and reception for a plurality of UEs. The eNB transmits downlink scheduling information with respect to downlink data to notify a corresponding UE of data transmission time/frequency domains, coding, data size, and Hybrid Automatic Repeat and reQuest (HARQ)-related information. In addition, the eNB transmits uplink scheduling information with respect to uplink data to inform a corresponding UE of available time/frequency domains, coding, data size, and HARQ-related information. An interface for transmitting user traffic or control traffic may be used between eNBs. A Core Network (CN) may include the AG, a network node for user registration of the UE, and the like. The AG manages mobility of the UE on a Tracking Area (TA) basis, wherein one TA consists of a plurality of cells.
Although radio communication technology has been developed up to LTE based on Wideband Code Division Multiple Access (WCDMA), demands and expectations of users and service providers continue to increase. In addition, since other radio access technologies continue to be developed, new technical evolution is required to secure future competitiveness. Decrease of cost per bit, increase of service availability, flexible use of a frequency band, simple structure, open interface, and suitable power consumption by a UE are required.
Recently, 3GPP has been establishing a standard task for a subsequent technique of LTE. In this disclosure, such a technique is referred to as ‘LTE-A’. One of the main differences between an LTE system and an LTE-A system is system bandwidth and the introduction of a relay node.
The LTE-A system is aimed at supporting broadband of a maximum of 100 MHz and, to this end, the LTE-A system is designed to use a carrier aggregation or bandwidth aggregation technique achieving broadband using a plurality of frequency blocks.
Carrier aggregation employs a plurality of frequency blocks as one large logical frequency band in order to use a wider frequency band. A bandwidth of each frequency block may be defined based on a bandwidth of a system block used in the LTE system. Each frequency block is transmitted using a component carrier.
Although aperiodic Sounding Reference Signal (SRS) transmission has been discussed to more effectively use a plurality of uplink component carriers employed in the 3GPP LTE-A system of a future communication system and to more accurately estimate an uplink channel, a detailed method for supporting SRS transmission has not been proposed up to now.